1. Field of the Invention
The present invention relates to a world wide power supply apparatus, particularly to a world wide power supply apparatus which can reduce the power consumption and can improve the reliability of a power supply apparatus by constituting a switch relay for switching a full-wave rectification or voltage doubling rectification mode.
2. Description of the Prior Art
A world wide commercial AC power is classified largely as 110 V system and 220 V system. But, because there is a large deviation according to the level of quality management of the AC power by countries, a world wide power supply apparatus has to cover the range of AC 80 V 280 V.
Therefore, a conventional world wide power supply apparatus is constituted to perform voltage doubling rectification when rectifying a commercial AC power of 110 V, and to perform a full-wave rectification in case of rectifying 220 V.
FIG. 1 shows a conventional world wide power supply apparatus. A commercial AC voltage 10 is connected to a voltage doubler rectifier circuit 14 via a full-wave rectifier circuit 12. A rectified DC signal VIN is switched to a high frequency signal by a switching mode control chip at a primary part of a power transformer 18. The switched high frequency signal is output via a rectifier circuit through a secondary part of the power transformer 18.
In case of 110 V commercial AC voltage, a voltage doubler rectifier circuit 14 is selected by that a triac TR is turned on by a voltage detection circuit 16. Therefore, a positive half wave flows through a diode, a first capacitor C1 and the triac TR (shown in solid line) and then is charged to the first capacitor C1. A negative half wave flows through the triac TR, a second capacitor C2, a ground and a diode (shown in dashed line) and then is charged to the second capacitor. Therefore, a DC voltage VIN comes out as a doubled input voltage by a serial connection of the first and second capacitors C1 and C2. That is, in case of 110 V, the DC voltage comes out as 220 V.
In case that a commercial AC voltage is 220 V, the triac TR is turned on by the voltage detection circuit 16 and thus a full-wave rectifier circuit 12 is selected. Therefore, since an input AC voltage is full-rectified through the full-wave rectifier circuit 12, the DC voltage VIN becomes 220 V.
The prior art world wide power supply apparatus like the above-mentioned uses the triac TR and the voltage detection chip 16 to switch the full-wave rectification/voltage doubling rectification. The drawbacks are that the customized voltage detection chip 16 generates a strong surge voltage to the commercial AC power, or can be operated erroneously by being outside of the range of a control region in case of abnormal transient-cause forced outage. That is, because, in case that the triac TR is turned on due to the erroneous operation in a 220 V region, an AC 220 V is voltage doubling-rectified and thus 440 V appears as the DC voltage VIN, the high voltage like the above-mentioned can damage severely the switching mode control chip 20 and capacitors C1 and C2, and it is a concern that the above-mentioned conditions can cause a problem like an outbreak of a fire.
Therefore, in order to prevent the problem, a double or triple safety apparatus is needed but danger remains unchanged according to the reliability of a protection circuit.
Also, because it is necessary to supply a current for the operation of a voltage doubler circuit itself from a very high voltage input, there will be a large power loss. About 80% of a self power loss of the whole voltage doubler rectifier circuit is generated by a gate driving of a triac. Therefore, a high-priced sensitive triac is required to drive with a low current, which can be a main cause of price markup.
Because an excessive power supply noise is created in an input AC and, a high voltage resistant triac has to be used which can endure the transient voltage, and this can be a main cause of price markup. Also, a triac is required which satisfies two contradictory conditions of requiring a low gate current and at the same time having a strong endurance to noise. Therefore, a gate driving circuit must eliminate any noise generated in a gate terminal. A non-trigger voltage of a triac is about 0.2 V. Therefore, it is impossible to eliminate noise to desired extent.
It is an object of the present invention to provide a world wide power supply apparatus which can reduce a power consumption, can keep the cost down and can improve the reliability of a power supply apparatus, by constituting a switching device switching a full-wave rectification and a voltage doubling rectification mode with a relay instead of a triac.
According to one aspect of the present invention, the apparatus of the present invention comprises a full-wave rectifier circuit having a pair of AC input terminals and a pair of DC output terminals, a pair of capacitors connected in series between a pair of DC output terminals, a relay switch connected between a common connection point of capacitors and one of the pair of AC input terminals and a relay driving circuit driving the above relay switch so that the relay switch can operate in a voltage doubling mode by turning on the relay switch in case that an AC voltage supplied to a pair of AC input terminals is a low voltage, and can operate in a full-wave rectification mode by turning off the relay in case of a high voltage.